Solder bonding using a solder material is used as a method for mounting a semiconductor element on a mounting substrate in a semiconductor device. Pb—Sn-based materials are used as such solder materials. These days, with the movement toward Pb-free products, also Sn—Ag-based materials and Sn—Ag—Cu-based materials are used.
For the bonding of a semiconductor element and a mounting substrate placed in a high temperature environment in a semiconductor device, Pb—Sn-based solder is widely used even at present when movement toward Pb-free products is in progress. It is important to improve the long-term reliability of the semiconductor device when it is continued to be used in a high temperature environment.